Hey guys, I'm sorry I let this drop off my radar
but I finally did use my Oben monopod with 3 leg support this evening.
I went out to a local pond with my K-3 II + battery grip,
Tamron 400/4 Adaptall +
1.4x-L teleconverter, and Oben monopod. The lens is similar in size and weight to the DFA 150-450mm. I made a few snaps with the monopod without using the 3 legs, and the rest with. Even angled slightly downward on rough terrain, the legs provided much more stability than without. Not enough to let go of the camera, but enough to stabilize it by 1 stop compared with using the monopod with only the pointed end.
I have yet to get a head for the monopod, so I simply screwed it into the lens' tripod mount.
Obviously, carrying the monopod - I nearly just typed "tripod" - with the legs extended makes it far more cumbersome. I've only been out with it twice, but I can tell already that my usage pattern will be to use it with the legs retracted, and then when I feel there's an opportunity to spend a few minutes with my subject the legs will come out.
It takes about 30-40 seconds to invert the camera/lens/monopod combo, extract and attach the legs, and re-orient everything.
GBH @ 50 yards